Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. In addition, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery module having a plurality of battery cells electrically connected to each other because high output and large capacity are necessary for the middle or large-sized devices.
Preferably, the middle or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle or large-sized battery module. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the weight of the pouch-shaped battery is small, and the manufacturing cost of the pouch-shaped battery is low.
In addition, the battery module is a structural body including a plurality of battery cells which are combined with each other with the result that the safety and operating efficiency of the battery module may be lowered when overvoltage, overcurrent, and/or overheating occur in some of the battery cells. Consequently, a sensing means for sensing the overvoltage, overcurrent, and overheating of the battery cells is needed. For example, a voltage sensor may be connected to the battery cells so as to sense and control the operation of the battery cells in real time or at predetermined time intervals.
In connection with this matter, a secondary battery is being used as a power source for vehicles as a result of the extension of an application range of the secondary battery. For this reason, it is necessary to maintain a state in which the sensing means is stably connected to the battery module even when strong impact or vibration is applied to the battery module.
In a conventional battery module, therefore, voltage of the battery cells is sensed in a mechanical coupling manner using bolts, rivets, or clips or in a point contact manner using springs.
In the mechanical coupling manner using bolts, bus bars are coupled to electrode leads of the battery cells by bolts at a predetermined torque. In this coupling manner, the bolts may be loosened due to external force such as vibration. Consequently, reflection and management of an optimum torque value are necessary so as to prevent the bolts from being loosened. In addition, stress is concentrated on electrode leads, which are relatively weak, and the electrode leads are fatigued, with the result that holes formed in electrode terminal connection parts such that the bolts are coupled through the holes may easily break.
In the mechanical coupling manner using rivets, on the other hand, electrode leads of the battery cells are connected to each other via the rivets. In this coupling manner, a loosening degree of the rivets due to external force is less than in the mechanical coupling manner using bolts. Even in this coupling manner, however, it is necessary to form holes in electrode terminal connection parts such that the rivets are inserted through the holes, with the result that breakage similar to the breakage occurring in the mechanical coupling manner using bolts may occur.
That is, the mechanical coupling manner has a problem in that, when external force, such as vibration, is applied to a battery module, a sensing defect occurs due to loosening of the bolts, and, when external force is applied to the battery module, stress is concentrated on holes formed in the electrode terminals of the battery cells such that the bolts or the rivets are inserted through the holes, with the result that breakage of the holes occurs.
In the point contact manner using springs, sensing is performed by direct point contact between the electrode leads of the battery cells and the springs. That is, sensing through the overall surface is not performed but voltage of a corresponding battery cell is sensed using a specific point. In this point contact manner, however, the sensing surface may be separated due to external force, or foreign matter may be introduced between sensing parts, with the result that it may not be possible to perform stable voltage sensing.
In recent years, a mechanical fastening manner using clips, in which sensing clips are mounted at a battery module case, and electrode lead connection parts are inserted into the clips for achieving mechanical fastening, has been used for some battery modules. However, the mechanical fastening manner using the clips has problems in that cost of components is high, whereby manufacturing cost of the battery module is increased, and a fastening process is complicated, whereby manufacturing processability is lowered.
Therefore, there is a high necessity for a voltage sensing member having a specific structure that is capable of stably sensing voltage of battery cells with respect to electrode leads of the battery cells while easily solving the above-mentioned problems and a battery module including the same.